Nuclear Physics News

Laboratory Profile: Jefferson Lab

Contributed by Lawrence S. Cardman

After more than a decade of planning and preparation, nuclear physics experiments using the 4 GeV Continuous Electron Beam Accelerator Facility (CEBAF) began in November 1995 at the newly named Thomas Jefferson National Accelerator Facility in Newport News, Virginia. The laboratory was formally named at its May 1996 dedication for Thomas Jefferson (1743-1826), the Virginia polymath and U.S. president who was an early leader in promoting science in the United States.

Jefferson Lab's research program is focused on bridging the hadronic and quark descriptions of nuclear matter. An active user group with over 1,000 members helped plan the physics program and design and build the experimental equipment. The laboratory's Program Advisory Committee (PAC) has convened regularly since 1987, first to review and endorse experimental equipment plans and then to review research proposals. The PAC's recommendations have led to approval for 80 collaborative experiments involving 596 senior scientists from 116 institutions in 23 countries. Completing this initial program will take approximately three years of beam time in each of the facility's three large experimental halls.

As most experiments at electron facilities require dedicated use of beam, the accelerator has been designed to provide independent continuous-wave (cw) beams to three experimental areas simultaneously. Halls A, B, and C have been built with equipment designed to provide complementary capabilities for probing nucleon and nuclear structure. The first of these, Hall C, has been in operation since November 1995; as of October 1996 the first three experiments have been completed and two more are in progress. Commissioning is well underway in Hall A and imminent in Hall B.

The early operational performance of the cw superconducting radio-frequency (SRF) accelerator can only be described as remarkable. Over 2,500 hours of beam have been delivered to experimental targets, and the accelerator has operated with 67% availability. Operation at the full design energy of 4 GeV is now routine at up to one-third the 200 mA design current, and the beam characteristics are superb: the transverse emittance (less than 10-9 m-r) and the measured energy spread (2.8 x 10-5) both exceed the accelerator design specifications. This performance has supported the rapid turn-on of the experimental program.